The invention relates to a fast neutron nuclear reactor having a storage structure independent of the core structure.
It more particularly applies to a fast neutron reactor cooled by means of a liquid metal, e.g. sodium. Such a reactor has a vertically axed main vessel containing the liquid cooling metal in which is immersed the reactor core. The core is constituted by a group of elongated boxes, each containing a bundle of sheathed needles or rods containing the fissile and/or fertile material. At the upper end of said boxes, there is a gripping head, which makes it possible to raise and transfer them. At the bottom thereof, there is a base or foot making it possible to position them in a horizontal support structure, which rests on a flooring fixed to the bottom of the vessel.
During the life of the reactor, it is necessary to periodically replace the spent assemblies by new assemblies. This handling operation is generally carried out by means of an arm or a grapnel, which transfers the assemblies into a loading and unloading container, which makes it possible to remove the assemblies from the reactor vessel.
In the known solutions, the extraction from the core of irradiated assemblies with a view to their replacement by new assemblies, is followed by storage within the vessel and outside the core in an area where the assembly in question can be partly cooled and lose part of its residual activity before being removed from the main vessel for storing outside, where its activity continues to decrease.
However, in the present state of the art, the storage area forms an integral part of the core structure. This leads to an increase in the dimensions of said structure and particularly an increase in its diameter. Among the other disadvantages caused by it, it makes it necessary to provide in the slab sealing the vessel, an opening which is sufficiently large to permit the passage of the structure.